Merge to M81: Update transport overhead the first time the network co…

…nnects.

This fixes a bug where transport_overhead_bytes_per_packet_ is sometimes
not set and therefore not included in the BWE.

(cherry picked from commit b4cdd62)

Bug: webrtc:11359, chromium:1053421
Change-Id: Id3593299c6bcd7ce3c44a7b148c202240b3f1981
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168525
Reviewed-by: Christoffer Rodbro <crodbro@webrtc.org>
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Commit-Queue: Jakob Ivarsson <jakobi@webrtc.org>
Cr-Original-Commit-Position: refs/heads/master@{#30522}
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168723
Cr-Commit-Position: refs/branch-heads/4044@{#4}
Cr-Branched-From: be99ee8-refs/heads/master@{#30432}

call/rtp_transport_controller_send.cc

@@ -259,6 +259,10 @@ void RtpTransportControllerSend::OnNetworkRouteChanged(
   auto kv = result.first;
   bool inserted = result.second;
   if (inserted) {
+    task_queue_.PostTask([this, network_route] {
+      RTC_DCHECK_RUN_ON(&task_queue_);
+      transport_overhead_bytes_per_packet_ = network_route.packet_overhead;
+    });
     // No need to reset BWE if this is the first time the network connects.
     return;
   }